1. Field of the Invention
This invention relates to an indicating apparatus and method of manufacture. More particularly, this invention relates to devices for indicating a change in condition by producing a color change and methods of manufacture therefor.
2. Description of the Related Art
In the preparation and storage of foodstuffs, both raw and cooked, it is desirable to have some manner of indicating whether frozen items have previously been thawed. This is true in both home and commercial (such as a grocery store, supermarket, or restaurant) settings. Such information is useful from health, safety, and nutritional standpoints.
In the healthcare industry, it is well known that some vaccines, blood, various medications, etc. are temperature-sensitive. Because such materials may not function properly if frozen and then thawed, it is not only desirable but also essential to know whether these materials have been previously frozen. Similarly, it would be very beneficial to know whether material, which is stored frozen, is allowed to thaw and subsequently is refrozen.
Maximum-minimum thermometers may be used to indicate the range of temperatures to which an item has been exposed. However, the use of such apparatus with every item in a frozen food department of a grocery store or supermarket, or with every container of vaccine, blood, drug, or other heat fragile item, is both impracticable and prohibitively costly.
Freeze-thaw indicators are known. For example, the Applicant""s previous patent, U.S. Pat. No. 4,163,427, which is incorporated by reference herein in its entirety, discloses an apparatus in which melting ice is used to activate a dye formation in producing a color indication of thawing. The present invention uses a pigment rather than a dye to indicate a freeze-to-thaw transition. The use of a pigment allows for a greater clarity of indication, a reduced chance of error, and a reduction in manufacturing costs.
Another known device is marketed under the name xe2x80x9cColdMark Freeze Indicators.xe2x80x9d This device comprises three liquids that provide a color change upon extended exposure below a certain temperature and another color change upon extended exposure above the temperature. However, this device is much larger than, and much more expensive than, the device of the present invention.
It is an object of the present invention to provide an apparatus for indicating a change in condition.
It is a further object of the present invention to provide an apparatus for indicating a transition from a frozen condition to a thawed condition.
It is a further object of the present invention to provide an apparatus for indicating a change in time.
It is a further object of the present invention to provide an improved indicator apparatus.
It is a further object of the present invention to provide a reliable indicator apparatus.
It is a further object of the present invention to provide an inexpensive indicator apparatus.
It is a further object of the present invention to provide an indicator apparatus that uses a pigment indicator.
It is a further object of the present invention to provide an indicator apparatus that can use a single frangible capsule.
It is a further object of the present invention to provide an indicator apparatus that can be used to monitor a small item, such as an individual vaccine vial.
It is a further object of the present invention to provide an indicator apparatus that creates a brilliant color upon a freeze-to-thaw event.
The apparatus of the present invention indicates a freeze-to-thaw condition using two reactants that combine to produce a pigment. A pigment is insoluble in the medium in which it is applied, while a dye is soluble. The use of a pigment is superior to the use of a dye since, for example, a pigment can produce a more brilliant color with smaller amounts of each reactant. Additionally, pigment reactants are less likely to produce a color change with anything other than the complementary reactant.
A housing is provided. One or more capsules are provided within the housing. As used herein, xe2x80x9ccapsulexe2x80x9d refers to any closed receptacle and includes microcapsules. A first reactant and a liquid are provided inside the capsule. The liquid is chosen such that it expands upon freezing. The capsule is designed such that when the liquid freezes and expands, the capsule fractures. A second reactant is provided within the housing. The location of the second reactant and the means of coupling (if any) to the housing may take various forms. For example, the second reactant may take the form of a coating on the housing. The second reactant may also be mixed with an adhesive for coupling the second reactant to the housing. The second reactant may also take the form of a coating on the outside of the capsule. The second reactant may be coupled to a piece of material, such as paper, and the material placed inside the housing.
When the capsule and the liquid located therein freeze, the liquid expands. Since the capsule does not expand upon freezing, the expansion of the liquid fractures the capsule. When the capsule is subsequently thawed, the liquid melts, releasing the first reactant. The first and second reactants then combine to form a pigment. The pigment is a brilliant color that is chosen to be a different color than the housing, allowing a person viewing the freeze-thaw indicator device to quickly and easily know whether the device has been previously frozen and thawed.
The device of the present invention may be attached to any number of items in order to determine whether the items have been frozen and thawed. Exemplary preferred items to monitor include, but are not limited to, vaccines, other medications, food, and other temperature-sensitive items.
The device of the present invention may also be initiated manually. Rather than fracture via expansion upon freezing, the device of the current invention can be initiated by manually fracturing the capsule, thus allowing the device to be used as a time-temperature indicator.